Hydrogen Generator with Improved Fluid Distribution

ABSTRACT

The invention is a hydrogen generator including a housing, a reaction area, a fluid reservoir, a pellet comprising a first reactant within the reaction area, a fluid comprising a second reactant within the fluid reservoir, a fluid flow path between the fluid reservoir and the reaction area, and a hydrogen outlet. The fluid flow path comprises a follower assembly biased toward the pellet, the follower assembly includes an articulated joint and a follower, and the second reactant can react with the first reactant in the reaction area to produce hydrogen gas and byproducts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/511,748, filed on Jul. 26, 2011.

FIELD OF THE INVENTION

This invention relates to a hydrogen gas generator, particularly ahydrogen generator for a fuel cell system.

BACKGROUND

Interest in fuel cell batteries as power sources for portable electronicdevices has grown. A fuel cell is an electrochemical cell that usesmaterials from outside the cell as the active materials for the positiveand negative electrode. Because a fuel cell does not have to contain allof the active materials used to generate electricity, the fuel cell canbe made with a small volume relative to the amount of electrical energyproduced compared to other types of batteries.

Fuel cells can be categorized according to the types of materials usedin the positive electrode (cathode) and negative electrode (anode)reactions. One category of fuel cell is a hydrogen fuel cell usinghydrogen as the negative electrode active material and oxygen as thepositive electrode active material. When such a fuel cell is discharged,hydrogen is oxidized at the negative electrode to produce hydrogen ionsand electrons. The hydrogen ions pass through an electricallynonconductive, ion permeable separator and the electrons pass through anexternal circuit to the positive electrode, where oxygen is reduced.

In some types of hydrogen fuel cells, hydrogen is formed from a fuelsupplied to the negative electrode side of the fuel cell. In other typesof hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from asource outside the fuel cell. A fuel cell system can include a fuel cellbattery, including one or more fuel cells, and a hydrogen source, suchas a fuel tank, a hydrogen tank or a hydrogen generator. In some fuelcell systems, the hydrogen source can be replaced after the hydrogen isdepleted. Replaceable hydrogen sources can be rechargeable ordisposable.

A hydrogen generator uses one or more reactants containing hydrogen thatcan react to produce hydrogen gas. The reaction can be initiated invarious ways, such as hydrolysis and thermolysis. For example, tworeactants can produce hydrogen and byproducts. An accelerator and/or acatalyst can be used to increase the rate of reaction or catalyze thereaction. When the reactants react, reaction products including hydrogengas and byproducts are produced.

Some types of hydrogen generators include a first reactant in solid formand a second reactant in fluid form. The first reactant can be formedinto one or more solid forms, referred to herein as pellets. The firstand second reactants are initially separated, and the second reactant istransported to come in contact with the first reactant, and thereactants react to produce hydrogen gas. Transport of the fluid can becontrolled so that hydrogen is produced as need by an external devicesuch as a fuel cell stack.

It is desirable for the first and second reactants to react efficientlyand completely to provide the maximum quantity of hydrogen for a givenhydrogen generator size. To accomplish this, good contact is requiredbetween the first and second reactants throughout the use of thehydrogen generator. Accumulation of byproducts around unconsumedportions of the pellet and accumulation (e.g., pooling) of fluid canboth interfere with good contact between unreacted first and secondreactants. Prior attempts have been made to improve the contact betweenthe first and second reactants by providing good distribution of fluidto the pellet and removing byproducts from the vicinity of unconsumedportions of the pellet. Examples of such attempts are disclosed in U.S.Pat. Nos. 3,820,956 and 7,097,813, and in US Patent Publication Nos.2008/0216906, 2009/0274595, 2008/0014481 and 2009/0104481. However,prior hydrogen generators have had a variety of shortcomings, andfurther improvement is desirable.

In view of the above, it is desirable to provide a hydrogen gasgenerator that can produce a maximum amount of hydrogen per unit volumeof the hydrogen generator. Excellent reaction efficiency, with maximumuse of reactants is desired, as is utilization of the internal volume ofthe hydrogen generator for all components. It is also desirable for thehydrogen generator to have a simple design, be easily manufactured andhave a low cost.

SUMMARY

The above objects are met and the above disadvantages of the prior artare overcome by the present invention. One aspect of the presentinvention is a hydrogen generator comprising a housing, a reaction area,a fluid reservoir, a pellet comprising a first reactant within thereaction area, a fluid comprising a second reactant within the fluidreservoir, a fluid flow path between the fluid reservoir and thereaction area, and a hydrogen outlet. The fluid flow path includes afollower assembly that is biased toward the pellet, the followerassembly comprises an articulated joint and a follower, and the secondreactant can react with the first reactant in the reaction area toproduce hydrogen gas and byproducts.

The hydrogen generator can include one or more of the followingfeatures:

-   -   the articulated joint includes at least one of a ball joint, a        universal joint and a flexible joint in which a component can        bend;    -   the follower is pivotable;    -   the follower includes a plurality of fluid outlets on a face        facing the pellet;    -   the follower assembly includes a fluid control mechanism        configured to selectively adjust fluid flow through the        plurality of fluid outlets based on an orientation of the        follower; the fluid control mechanism can be part of the        follower; the fluid control mechanism can include a plurality of        valves;    -   a fluid dispersion layer is disposed on a face of the follower;        the fluid dispersion layer can include a porous, compressible        material;    -   the hydrogen gas is separated from the byproducts before passing        through the hydrogen outlet;    -   the hydrogen gas and the byproducts flow past the follower        before passing through the outlet;    -   the hydrogen gas and the byproducts flow through spaces around        the follower;    -   the hydrogen gas and the byproducts flow through openings in the        follower;    -   the hydrogen generator includes a byproduct containment area;        the byproduct containment area can be separated from the        reaction area by the follower; the byproduct containment area        can separate the reaction area and the fluid reservoir; the        reaction area and the byproduct containment area can be in a        volume exchanging relationship; the fluid reservoir and the        byproduct containment area can be in a volume exchanging        relationship; the byproduct containment area can contain one or        more filter members; the one or more filter members can include        an initially compressed filter that can expand as the byproduct        containment area enlarges;    -   the fluid reservoir includes a flexible container;    -   the reaction area is disposed adjacent to the fluid reservoir;    -   the fluid is transportable through the fluid flow path by a        pump, either within or outside the hydrogen generator;    -   the fluid is transportable through the fluid flow path by        pressure applied to the fluid reservoir, by a biasing member or        a gas;    -   the follower is biased by a spring;    -   the first reactant includes a chemical hydride, preferably a        borohydride, more preferably sodium borohydride;    -   the pellet further includes a reaction accelerator, preferably        an acid, more preferably one or more of malic, citric, succinic        and tartaric acid;    -   the pellet further includes a catalyst;    -   the fluid further includes a reaction accelerator, preferably an        acid, more preferably one or more of malic, phosphoric, succinic        and acetic acid; and    -   the fluid further includes a catalyst.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

Unless otherwise specified, the following definitions and methods areused herein:

-   -   “effluent” means non-gaseous reaction products and unreacted        reactants, solvents and additives;    -   “expand” when used in describing a filter means for the filter        material to simultaneously increase in volume, increase in        porosity and decrease in density and pertains only to the        material of which the filter is made;    -   “initial” means the condition of a hydrogen generator in an        unused or fresh (e.g., refilled) state, before initiating a        reaction to generate hydrogen;    -   “volume exchanging relationship” means a relationship between        two or more areas, chambers or containers within a hydrogen        generator such that a quantity of volume lost by one or more of        the areas, chambers or containers is simultaneously gained by        one or more of the other areas, chambers or containers; the        volume thus exchanged is not necessarily the same physical        space, so volume lost in one place can be gained in another        place.

Unless otherwise specified herein, all disclosed characteristics andranges are as determined at room temperature (20-25° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of a hydrogen generator;

FIG. 2 is a plan view of a side of the hydrogen generator in FIG. 1;

FIG. 3 is a partial sectional view of the hydrogen generator sectionalalong line 3-3 in FIG. 2;

FIG. 4 is a sectional view of the follower assembly in the hydrogengenerator in FIG. 3; and

FIG. 5 is a cross-sectional view of the follower assembly in FIG. 4along line 5-5.

DESCRIPTION

Hydrogen gas can be provided by the hydrogen generator to a hydrogenconsuming apparatus such as a hydrogen fuel cell stack. The hydrogenconsuming apparatus and the hydrogen generator can be incorporated intoa system that includes controls for controlling the transfer of liquidfrom the liquid reservoir to the reaction area of the hydrogengenerator.

A hydrogen generator according to the invention includes a housingcontaining two reactants, a first reactant in a solid form, and a secondreactant in a fluid form, such as a liquid. Initially the first andsecond reactants are separate from each other. The first reactant iscontained within a reaction area, and the second reactant is containedwithin a fluid reservoir. The composition containing the first reactantcan be in the form of a powder, granules, agglomerates and the like, orit can be formed (e.g., by compressing or molding) into one or moresolid shapes, such as a pellet, tablet, cake and the like. Preferablythe first reactant is formed into a solid shape. For convenience, thesolid is referred to below as a pellet, but it is understood that anysolid form can be used, whether formed into a solid shape or not. Thepellet can consist of only the first reactant, or it can contain othersolid ingredients as well, as described in further detail below. Thesecond reactant is contained in a fluid. The second reactant can be afluid itself, or it can be contained in a fluid, such as by dissolvingin a liquid or suspending in a suspension or gel. The fluid can consistof only the second reactant, or it can contain other ingredients aswell, as described in further detail below.

The fluid is transported from the fluid reservoir, through a fluid flowpath, to the reaction area, where the second reactant can come incontact and react with the first reactant. A catalyst can be used insome embodiments to catalyze the reaction. In some embodiments the rateof reaction can be controlled by other ingredients in one or both of thepellet and the fluid, or by other means such as heating or cooling oradding other materials to the reaction area. Hydrogen gas and byproductsare produced in the reaction area, and the hydrogen gas is separatedfrom the byproducts and other liquids and solids (e.g., unconsumedpellet and fluid components) and can exit the hydrogen generator througha hydrogen outlet.

In some embodiments the hydrogen generator includes a byproductcontainment area, separate from the reaction area and reservoir, intowhich the hydrogen gas and byproducts can flow from the reaction area.It is advantageous for components of the hydrogen generator to be in avolume exchanging relationship such that as the contents of onecomponent are emptied, another component can expand to accommodatematerials that are being added. For example, the byproducts containmentarea can be in a volume exchanging relationship with one or both of thefluid reservoir and the reaction area. If there is no byproductscontainment area and byproducts are accumulated within the reactionarea, the reaction area can be in a volume exchanging relationship withthe fluid reservoir; this can be advantageous when the volume of thereaction products is greater than the combined volumes of the reactants.Volume exchange can contribute to the hydrogen generator's volumeefficiency (the volume of hydrogen that can be produced divided by thevolume of the hydrogen generator).

Fluid is transported from the fluid reservoir to the reaction area viathe fluid flow path, which can be entirely within the hydrogengenerator, or a portion can be located externally. Various methods canbe used—examples include a pump, which can be internal or external tothe hydrogen generator; pressure applied to the fluid reservoir, by abiasing member, hydraulic pressure or pneumatic pressure; or bypressurizing the fluid reservoir with a gas. The flow path can includevarious components such as pipes, tubes, valves and the like.

The fluid reservoir includes a liquid impermeable container. Thecontainer can be rigid or flexible. A flexible container can becomesmaller (e.g., by collapsing and/or contracting) as liquid istransported out of the reservoir, so that space initially occupied bythe reservoir can be made available to an enlarging byproductscontainment area. Examples of types of flexible containers includecontainers with walls having accordion folds, similar to a bellows;elastic containers that can stretch and contract in response to changesin pressure like a balloon; and containers made of non-elastic materialsthat are not rigid but also do not stretch or contract to a greatextent. Examples of flexible, films include polyethylene, polypropylene,polyvinylchloride, rubber, latex, silicone, Viton, polyurethane,neoprene, buna-N, polytetrafluoroethylene, expandedpolytetrafluoroethylene, perfluoroelastomers, and fluorosilicone.

The reaction area can have rigid walls to contain the pellet, generallyon all sides but one. A follower is disposed on one side or end,adjacent to a surface of the pellet, and is biased against the pellet.It can be biased by a biasing member, such as a spring or ahydraulically or pneumatically operated mechanism. The follower caninclude a plurality of fluid outlets that are part of the fluid flowpath from the fluid reservoir. The fluid outlets can be spaced on theface of the follower to provide good distribution of the fluid to thesurface of the pellet.

The surface of the pellet facing the follower may not be consumed evenlyduring the reaction of the reactants. This can be the result of fluidflow due to gravity within the reaction area, non-uniform composition ofthe pellet, or other factors. With a follower having a fixedorientation, the follower may consequently be in contact with only asmall portion of the surface of the pellet, resulting in reducedhydrogen generation, which in turn can initiate an increased rate offluid supply to maintain the required hydrogen supply rate, andunreacted fluid can accumulate in areas within the reaction area thatare not in good contact with unreacted first reactant.

According to the invention, the follower is articulated so the face ofcan move. As the follower is biased against the pellet, if the adjacentsurface of the pellet is not parallel to the plane of the follower face,the follower can pivot to an orientation that will maximize the contactarea between the follower and the pellet. For example, the portions ofthe pellet surface that have been consumed the least will project fromthe bulk of the pellet to a greater degree. As the follower is biasedagainst the pellet, non-uniform contact between the follower face andthe pellet can cause the follower to move, such as by pivoting. This canhelp orient the follower face to maximize contact between the followerface and the surface of the pellet. The follower assembly includes anarticulated joint. Examples of articulated joints include but are notlimited to ball joints, universal joints and other flexible joints inwhich components can bend.

In some embodiments, the hydrogen generator includes a fluid controlmechanism configured to selectively control fluid flow through theplurality of fluid outlets based on the orientation of the follower. Forexample, if the follower face is in a plane that is perpendicular to thedirection of the biasing force, fluid flow will be equal to all of thefluid outlets. If the plane of the follower face is not perpendicular tothe direction of the biasing force, fluid flow will be greatest to theoutlet(s) on the portion(s) of the face that have been displaced themost in the direction opposite the direction of the biasing force, andfluid flow will be the least to the outlet(s) on the portion(s) of theface that have been displaced the most in the same direction as thedirection of the biasing force. The fluid control mechanism can bedisposed within the follower or elsewhere. A fluid control mechanismwithin the follower can include valves, with each valve controllingfluid flow to one or more outlets.

The follower face can include a dispersion layer that will allow thefluid to disperse between the fluid outlets. The dispersion layer ispreferably a porous material. It can be a material that is able to wickthe fluid to the surface of the pellet, such as a hydrophilic materialthat can wick an aqueous fluid. The dispersion layer can be acompressible material. This has the added advantage of being able tobetter conform to the surface of the pill than would a rigid surface.Examples of materials for the dispersion layer include woven andnonwoven fibrous materials, foams and felts. The dispersion layer can bemade from materials such as but not limited to nylon wools, siliconefoams, rubber foams, polyethylene foams, Viton foams, polyurethanefoams, neoprene foams, vinyl foams, acrylic fibers, polyimide foams,carbon felts, and polypropylene felts.

In some embodiments the hydrogen gas can exit the reaction area throughspaces around or openings through the follower. Preferably a byproductcontainment area is located on the opposite side of the follower fromthe reaction area. The hydrogen gas produced can carry the byproductsaway from the pellet and out of the reaction area to help preventblockage of the fluid from unreacted first reactant in the remainingpellet. It is advantageous for the byproducts containment area to belocated on the opposite side of the follower from the reaction areabecause the follower is close to the main reaction sites, and effluenthas to travel only a short distance to reach the byproduct containmentarea. The byproduct containment area can have a container, or spacewithin the hydrogen generator housing can serve as a byproductcontainment area. If the byproduct containment area has a container, itcan be a flexible container, and the byproduct containment area can bein a volume exchanging relationship with the fluid reservoir and/or thereaction area.

Hydrogen gas is separated from the byproducts and unconsumed reactantsbefore it leaves the hydrogen generator. This can be using one or morefilter members. Filter members can be included in one or more locationsin the hydrogen generator. For example, one or more filter elements canbe located where the hydrogen exits the reaction area, such as in spacesaround or openings through the follower. Filter members can be locatedwithin a byproduct containment area to help remove solids from theeffluent. Such filter elements can be initially compressed to occupy asmall volume and expand as the byproduct containment area expands toaccommodate more solids without becoming clogged. A final filter membercan be a hydrogen-permeable, liquid impermeable. A final filter elementcan be located between the reaction area and the hydrogen gas outlet,such as across the entrance to the hydrogen gas outlet, in a section ofa container surrounding the byproducts containment area, or it can bethe container surrounding the byproducts containment area, for example.Filter elements within the byproducts containment area can be porous,such as woven or nonwoven fibers, foams or felts. Filter elements withinthe byproduct containment area can be made of materials such as nylonwools, silicone foams, rubber foams, polyethylene foams, Viton foams,polyurethane foams, neoprene foams, vinyl foams, acrylic yarns,polyimide foams, carbon felts, polypropylene felts and the like. Thefinal filter element can be a hydrogen permeable, liquid impermeablematerial; examples include polymeric materials such as fluoropolymers(e.g. polytetrafluoroethylene and polytetrafluoroethylene derivatives)and expanded fluoropolymers (e.g., expanded polytetrafluoroethylene).

If the byproduct containment area is enclosed by a liquid impermeablecontainer, the hydrogen generator can also include a separate hydrogencontainment area. The hydrogen containment area can contain a limitedamount of hydrogen gas, as an initial supply of hydrogen that isavailable at startups, and/or to accumulate hydrogen gas that isproduced after transport of fluid to the reaction area is stopped.

The hydrogen generator can use a variety of reactants that can react toproduce hydrogen gas. At least one reactant is present in solid form inthe reaction area and at least one reactant is present in a fluid in thefluid reservoir. Examples of reactants for producing hydrogen gasinclude chemical hydrides, alkali metal silicides, metal/silica gels,water, alcohols, dilute acids and organic fuels (e.g., N-ethylcarbazoleand perhydrofluorene).

An alkali metal silicide is the product of mixing an alkali metal withsilicon in an inert atmosphere and heating the resulting mixture to atemperature of below about 475° C., wherein the alkali metal silicidecomposition does not react with dry O₂. Such alkali metal silicides aredescribed in US Patent Publication 2006/0002839. While any alkali metal,including sodium, potassium, cesium and rubidium may be used, it ispreferred that the alkali metal used in the alkali metal silicidecomposition be either sodium or potassium. Metal silicides including aGroup 2 metal (beryllium, magnesium, calcium, strontium, barium andradium) may also be suitable. In an embodiment, sodium silicide canreact with water to produce hydrogen gas and sodium silicate, which issoluble in water.

A metal/silica gel includes a Group 1 metal/silica gel composition. Thecomposition has one or more Group 1 metals or alloys absorbed into thesilica gel pores. The Group 1 metals include sodium, potassium,rubidium, cesium and alloys of two or more Group 1 metals. The Group 1metal/silica gel composition does not react with dry O₂. Such Group 1metal/silica gel compositions are described in U.S. Pat. No. 7,410,567B2 and can react rapidly with water to produce hydrogen gas. A Group 2metal/silica gel composition, including one or more of the Group 2metals (beryllium, magnesium, calcium, strontium, barium and radium) mayalso be suitable.

As used herein, the term “chemical hydride” is broadly intended to beany hydride capable of reacting with a fluid to produce hydrogen.Examples of chemical hydrides that are suitable for use in the hydrogengenerating apparatus described herein include, but are not limited to,hydrides of elements of Groups 1-4 (International Union of Pure andApplied Chemistry (IUPAC) designation) of the Periodic Table andmixtures thereof, such as alkaline or alkali metal hydrides, or mixturesthereof. Specific examples of chemical hydrides include lithium hydride,lithium aluminum hydride, lithium borohydride, sodium hydride, sodiumborohydride, potassium hydride, potassium borohydride, magnesiumhydride, calcium hydride, and salts and/or derivatives thereof. Othercompounds, such as nitrogen based compounds (e.g., ammonia borane) arealso suitable. In an embodiment, a chemical hydride such as sodiumborohydride can react with water to produce hydrogen gas and a byproductsuch as a borate. This can be in the presence of a catalyst, heat, adilute acid or a combination thereof.

Chemical hydrides can react with water to produce hydrogen gas andoxides, hydroxides and/or hydrates as byproducts. The hydrolysisreaction may require a catalyst or some other means of initiation, suchas a pH adjustment or heating. A catalyst or acid can be included in thesolid or in the fluid.

One or more catalysts can be used to catalyze the hydrogen producingreactions. Examples of suitable catalysts include transition metals fromGroups 8 to 12 of the Periodic Table of the Elements (e.g., Rh, Pd, Pt),as well as other transition metals including scandium, titanium,vanadium, chromium and manganese. Metal salts, such as chlorides,oxides, nitrates and acetates can also be suitable catalysts.

The rate of hydrogen generation can be controlled in a variety of ways,such as controlling of the rate at which liquid is transported to thereaction area, adjusting the pH, and making thermal adjustments. Therate of hydrogen generation can be controlled to match the need forhydrogen gas. A control system can be used for this purpose, and thecontrol system can be within or at least partially outside the hydrogengenerator.

Additives can be used for various purposes. For example, additives canbe included with a solid reactant as a binder to hold the solid materialin a desired shape or as a lubricant to facilitate the process offorming the desired shape. Other additives can be included in the fluidor the pellet to control pH. Examples of such additives include but arenot limited to acids (e.g., hydrochloric, nitric, sulfuric, citric,carbonic, boric, carboxylic, sulfonic, malic, phosphoric, succinic,tartaric and acetic acids or combinations thereof), or bases (e.g.,hydroxides such as those of Group 1 elements, ammonium, and organiccompounds; metal oxides such as those of Group 1 metals; and organic andmetal amines). Additives such as alcohols and polyethylene glycol basedcompounds can be used to prevent freezing of the fluid. Additives suchas surfactants, wetting agents and anti-foaming agents (e.g., glycols,polyglycols and polyols) can be used to control liquid surface tensionand reaction product viscosity to facilitate the flow of hydrogen gasand/or effluents. Additives such as porous fibers (e.g., polyvinylalcohol and rayon fibers) can help maintain the porosity of the pelletand facilitate even distribution of the fluid and/or the flow ofhydrogen and effluents.

In one embodiment a chemical hydride such as sodium borohydride (SBH) isa solid reactant, and water is another reactant. The chemical hydride isstored as a solid in the reaction area. If an increased rate of reactionbetween the chemical hydride and the water is desired, a solid acid,such as malic acid, can be mixed with the chemical hydride, or acid canbe added to the water. A chemical hydride can be formed into a solidmass, e.g., to reduce the amount of unreacted chemical hydride containedin the effluent that exits the reaction area. In an example, a mixtureincluding about 50 to 65 weight percent SBH, about 30 to 40 weightpercent malic acid and about 1 to 5 weight percent polyethylene glycolcan be pressed into a pellet. Optionally, up to about 3 weight percentsurfactant (anti-foaming agent), up to about 3 weight percent silica(anti-caking agent) and/or up to about 3 weight percent powderprocessing rheology aids can be included. The density of the pellet canbe adjusted, depending in part on the desired volume of hydrogen and themaximum rate at which hydrogen is to be produced. A high density isdesired to produce a large amount of hydrogen from a given volume. Onthe other hand, if the pellet is too porous, unreacted SBH can moreeasily break away and be flushed from the reaction area as part of theeffluent. One or more pellets of this solid reactant composition can beused in the hydrogen generator, depending on the desired volume ofhydrogen to be produced by the hydrogen generator. The ratio of water toSBH in the hydrogen generator can be varied, based in part on thedesired amount of hydrogen and the desired rate of hydrogen production.If the ratio is too low, the SBH utilization can be too low, and if theratio is too high, the amount of hydrogen produced can be too lowbecause there is insufficient volume available in the hydrogen generatorfor the amount of SBH that is needed.

It may be desirable to provide for cooling of the hydrogen generatorduring use, since the hydrogen generation reactions can produce heat.The housing may be designed to provide coolant channels. In oneembodiment standoff ribs can be provided on one or more externalsurfaces of the housing and/or interfacial surfaces with the fuel cellsystem or device in or on which the hydrogen generator is installed ormounted for use. In another embodiment the hydrogen generator caninclude an external jacket around the housing, with coolant channelsbetween the housing and external jacket. Any suitable coolant can beused, such as water or air. The coolant can flow by convection or byother means such as pumping or blowing. Materials can be selected and/orstructures, such as fins, can be added to the hydrogen generator tofacilitate heat transfer.

It may also be desirable to provide means for heating the hydrogengenerator, particularly at startup and/or during operation at lowtemperatures.

The hydrogen generator can include other components, such as controlsystem components for controlling the rate of hydrogen generation (e.g.,pressure and temperature monitoring components, valves, timers, etc.),safety components such as pressure relief vents, thermal managementcomponents, electronic components, and so on. Some components used inthe operation of the hydrogen generator can be located externally ratherthan being part of the hydrogen generator itself, making more spaceavailable within the hydrogen generator and reducing the cost byallowing the same components to be reused even though the hydrogengenerator is replaced.

The hydrogen generator can be disposable or refillable. For a refillablehydrogen generator, reactant filling ports can be included in thehousing, or fresh reactants can be loaded by opening the housing andreplacing containers of reactants. If an external pump is used to pumpliquid from the reservoir to the reaction area, an external connectionthat functions as a fluid reactant composition outlet to the pump canalso be used to refill the hydrogen generator with fresh liquid. Fillingports can also be advantageous when assembling a new hydrogen generator,whether it is disposable or refillable. If the hydrogen generator isdisposable, it can be advantageous to dispose components with lifeexpectancies greater than that of the hydrogen generator externally,such as in a fuel cell system or an electric appliance, especially whenthose components are expensive.

The liquid reservoir, reaction area and byproducts containment area canbe arranged in many different ways. As described above, by arranging thebyproducts containment area in a volume exchanging relationship with oneor both of the liquid reservoir and the reaction area, the hydrogengenerator can be more volume efficient and provide a greater amount ofhydrogen per unit of volume of the hydrogen generator. Otherconsiderations in arranging the components of the hydrogen generatorinclude thermal management (adequate heat for the desired reaction rateand dissipation of heat generated by the reactions), the desiredlocations of external connections (e.g., for hydrogen gas, liquid flowto and from an external pump), any necessary electrical connections(e.g., for pressure and temperature monitoring and control of fluidreactant flow rate), and ease of assembly.

FIG. 1 is a perspective view of an embodiment of a hydrogen generator 10with a housing 12 and a connector 14 for connecting to the rest of afuel cell system. The connector 14 includes a hydrogen outlet 20. It canalso include a liquid outlet 16 and a liquid inlet 18, when liquid istransported from a reservoir within the housing via an external pump,for example. Alternatively, means for moving the liquid out of thereservoir (e.g., an internal pump, an elastic liquid reservoir, meansfor applying pressure to the liquid reservoir, etc.) can be includedwithin the housing 12. The left side of the hydrogen generator 10 inFIG. 1 is shown in plan view in FIG. 2.

FIG. 3 is a partial sectional view along line 3-3 in FIG. 2. Acompartment 22 to accommodate a liquid reservoir (not show) is separatedfrom the remainder of the hydrogen generator 10 by a partition 24 thatincludes large perforations 26. In FIG. 3 a pellet 30 containing a solidreactant composition is disposed on the opposite side of the partitionfrom the liquid reservoir compartment 22, although other arrangementsare possible. The solid reactant composition can be powdered, granularor formed into a unitary or multiple structures, for example. Liquid istransported to a follower assembly 32 via a liquid transport tube 28.The follower assembly 32 includes a follower 34, having a surface facingthe pellet 30, and a ball joint including a ball 36. The followerassembly 32 is biased toward the pellet 30 so the follower 34 is incontact with the pellet 30. The follower assembly 32 can be biased by aspring 38. If the spring is a compression coil spring as shown in FIG.3, guides such as guides 40 and 42 can be included to keep the spring 38aligned and prevent it from buckling. In the embodiment shown in FIG. 3,the internal spring guide 40 is a part of the follower assembly 32, andthe external spring guide 42 is attached to the housing 12. Both guidesprings 40, 42 are hollow tubes with large openings in their walls.Other types of spring guides can be used.

Liquid is transported from the liquid reservoir, through the liquidtransport tube, to the follower assembly 32. The liquid flows to thesurface of the follower 34 facing the pellet 30, where it contacts andreacts with a solid reactant in the pellet 30 to produce hydrogen gasand byproducts. The hydrogen gas and byproducts flow around theperiphery of and/or through passageways through the follower 34 and intospaces within the housing 12, such as spaces around the spring 38 andspring guides 40, 42. If the hydrogen outlet 20 is on the same side ofthe partition 24 as compartment 22, the hydrogen gas can flow throughthe perforations 26 in the partition 24 and out of the hydrogengenerator 10 through the hydrogen outlet 20 as needed. Byproducts canalso flow through the perforations 26 and into unoccupied space in theliquid reservoir compartment 22. As shown in FIG. 3, the hydrogengenerator 10 is partially used. In an unused state the pellet 30 will belarger, the follower 34 will not be biased as far as shown in FIG. 3,and the spring 38 will be more fully compressed.

In the embodiment shown in FIG. 3, the area around the follower assembly32, spring 30 and spring guides 40, 42 and unoccupied space in theliquid reservoir compartment 22 serve as a byproduct containment area.The byproduct containment area is in a volume exchanging relationshipwith the reaction area—as the pellet is consumed during the hydrogengeneration, the volume of the reaction area becomes smaller and thevolume of the byproduct containment area becomes correspondingly larger.If the liquid reservoir includes a container that can collapse as liquidexits therefrom, the byproduct containment area can also be in a volumeexchanging relationship with the liquid reservoir.

The follower assembly 32 is shown in greater detail in FIGS. 4 and 5.FIG. 4 is a sectional view of the follower assembly 32, as viewed fromthe bottom of the hydrogen generator 10 in FIG. 3. The bottom surface ofthe follower 34 is also removed so internal features of the followerassembly 32 are visible. Liquid flows from the liquid transport tube 28into the ball 36 through fitting 44. The liquid flows through the ball36 as described below and through sleeves 46 and valves 48 to theopposite surface 60 of the follower 34.

FIG. 5 is a sectional view of the follower assembly 32 through line 5-5in FIG. 4. Liquid enters the ball 36 through the fitting 44 and flowsinto a cavity 50 surrounding the tip of the spring guide 40 connected tothe ball 36. Channels 52 lead to orifices 54 in the outer surface of theball 36. When the orifices 52 in the ball 36 are aligned withcorresponding orifices in valve seats 56 mounted in the follower 34, theliquid will flow through the valve seats 56 and into the sleeves 46 andvalves 48 to the opposite side 60 of the follower 32. As shown in FIG.5, the face 60 of the follower 34 is perpendicular to a longitudinalaxis of the spring guide 40. In this orientation, the orifices 54 of thechannels 52 in the ball 36 are partially aligned with correspondingorifices of the channels 58 in the valve seats 56 so that the flow ofliquid from the ball 36 through the valve seat 56 is limited. Becausethe junction of the ball 36 and the follower 34 constitutes a balljoint, the follower 34 can pivot relative to the ball 36. When thefollower 34 pivots, portions of the follower 34 are displaced downward(as oriented in FIG. 5), and those orifices of channels 58 that aredisplaced downward can become more completely aligned with thecorresponding orifices 54 of channels 52, thereby increasing the liquidflow through those valve seats 56. Conversely, the orifices of channels58 that are displaced upward can become nonaligned with thecorresponding orifices 54, blocking the flow of liquid through thosevalve seats 56. During use of the hydrogen generator 10, if the surfaceof the pellet 30 adjacent to follower face 60 is not evenly consumed,the less consumed portions will tend to press more against the follower34, causing it to pivot, increasing the flow of liquid to those portionsof follower face 60 that are displaced downward and decreasing the flowof liquid to those portions of the follower face 60 that are displacedupward relative to the perpendicular orientation of follower 34 shown inFIG. 5.

Because the follower assembly includes an articulated joint, the face ofthe follower adjacent to the pellet can move to correspond better withthe adjacent surface of the pellet. This can provide more uniformdistribution of liquid to the adjacent surface of the pellet, moreunifomi utilization of the reactant composition of the surface of thepellet adjacent to the follower, and, consequently, a more uniform rateof hydrogen generation, more complete utilization of the reactants and agreater total volume of hydrogen generated. These advantages can befurther enhanced by separately controlling liquid flow to differentareas on the face of the pellet, so more liquid is available where mostuseful and less liquid is available where least useful.

All references cited herein are expressly incorporated herein byreference in their entireties. To the extent publications and patents orpatent applications incorporated by reference contradict the disclosurecontained in the present specification, the present specification isintended to supersede and/or take precedence over any such contradictorymaterial.

It will be understood by those who practice the invention and thoseskilled in the art that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcept. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

1. A hydrogen generator comprising a housing; a reaction area; a fluidreservoir; a pellet comprising a first reactant within the reactionarea; a fluid comprising a second reactant within the fluid reservoir; afluid flow path between the fluid reservoir and the reaction area; and ahydrogen outlet; wherein: the fluid flow path comprises a followerassembly biased toward the pellet; the follower assembly comprises anarticulated joint and a follower; and the second reactant can react withthe first reactant in the reaction area to produce hydrogen gas andbyproducts.
 2. The hydrogen generator according to claim 1, wherein thearticulated joint comprises at least one of a ball joint, a universaljoint and a flexible joint in which a component can bend.
 3. Thehydrogen generator according to claim 1, wherein the follower ispivotable.
 4. The hydrogen generator according to claim 1, wherein thefollower comprises a plurality of fluid outlets on a face facing thepellet.
 5. The hydrogen generator according to claim 1, wherein thefollower assembly comprises a fluid control mechanism configured toselectively adjust fluid flow through the plurality of fluid outletsbased on an orientation of the follower.
 6. The hydrogen generatoraccording to claim 5, wherein the follower comprises at least a portionof the fluid control mechanism.
 7. The hydrogen generator according toclaim 5, wherein the fluid control mechanism comprises a plurality ofvalves.
 8. The hydrogen generator according to claim 1, wherein a fluiddispersion layer is disposed on a face of the follower.
 9. The hydrogengenerator according to claim 8, wherein the fluid dispersion layercomprises a porous, compressible material.
 10. The hydrogen generatoraccording to claim 1, wherein the hydrogen gas is separated from thebyproducts before passing through the hydrogen outlet.
 11. The hydrogengenerator according to claim 1, wherein the hydrogen gas and thebyproducts flow past the follower before passing through the outlet. 12.The hydrogen generator according to claim 1, wherein the hydrogen gasand the byproducts flow through spaces around the follower.
 13. Thehydrogen generator according to claim 1, wherein the hydrogen gas andthe byproducts flow through openings in the follower.
 14. The hydrogengenerator according to claim 1, wherein the hydrogen generator comprisesa byproduct containment area.
 15. The hydrogen generator according toclaim 14, wherein the byproduct containment area is separated from thereaction area by the follower.
 16. The hydrogen generator according toclaim 14, wherein the byproduct containment area separates the reactionarea and the fluid reservoir.
 17. The hydrogen generator according toclaim 14, wherein the reaction area and the byproduct containment areaare in a volume exchanging relationship.
 18. The hydrogen generatoraccording to claim 14, wherein the fluid reservoir and the byproductcontainment area are in a volume exchanging relationship.
 19. Thehydrogen generator according to claim 14, wherein the byproductcontainment area contains one or more filter members.
 20. The hydrogengenerator according to claim 19, wherein the one or more filter membersinclude an initially compressed filter that can expand as the byproductcontainment area enlarges.
 21. The hydrogen generator according to claim1, wherein the fluid reservoir comprises a flexible container.
 22. Thehydrogen generator according to claim 1, wherein the reaction area isdisposed adjacent to the fluid reservoir.
 23. The hydrogen generatoraccording to claim 1, wherein the fluid is transportable through thefluid flow path by a pump, either within or outside the hydrogengenerator.
 24. The hydrogen generator according to claim 1, wherein thefluid is transportable through the fluid flow path by pressure appliedto the fluid reservoir, by a biasing member or a gas.
 25. The hydrogengenerator according to claim 1, wherein the follower is biased by aspring.
 26. The hydrogen generator according to claim 1, wherein thefirst reactant comprises a chemical hydride, preferably a borohydride,more preferably sodium borohydride.
 27. The hydrogen generator accordingto claim 1, wherein the pellet further comprises a reaction accelerator,preferably an acid, more preferably one or more of malic, citric,succinic and tartaric acid.
 28. The hydrogen generator according toclaim 1, wherein the pellet further comprises a catalyst.
 29. Thehydrogen generator according to claim 1, wherein the fluid furthercomprises a catalyst.